Two eminent climate scientists discuss the policy debate. Their clash tells us much.

Summary: The climate policy debate heats up, as seen in this exchange between two climate scientists sparked by last week’s House hearing about climate change. It illuminates the areas of agreement and debate among scientists, which is an important aspect of the policy debate — but seldom mentioned by journalists.

Vapor Visualization of Hurricane in the Weather Research & Forecasting Model. From NCAR/UCAR.

The AMS was pleased to read in your opening remarks for the 29 March 2017 hearing …that you “believe the climate is changing and that humans play a role.” This captures, correctly, that people are causing climate to change. Your question on the extent of human influence is one that has been actively addressed by the scientific community on a continuing basis as we extend our knowledge of the climate system.

The scientific community has learned a great deal about Earth’s climate system over the past several decades, applying the scientific method rigorously to data analysis and to understanding the physical processes that affect global temperature and other aspects of climate change. Hypotheses have been developed and tested through scientific experiments. The results are then systematically challenged and synthesized through open debate in scientific conferences and the peer-reviewed literature. Critically, independent scientists are rewarded for uncovering flaws or shortcomings in the work of their colleagues, so the scientific process is inherently self-correcting over time. Results that withstand scrutiny, validation, and replication by independent researchers are the basis of our physical understanding of how the climate changes.

We can now say with very high levels of confidence, based on literally thousands of independent research efforts and multiple independent lines of evidence, that most of the warming our planet has experienced over the past 50 years is due to human activity. Indeed, to suggest that humans are not responsible for most of the warming we have experienced over the past 50 years indicates a disregard for the scientific process and the vast amount of testable evidence that has been amassed on this subject.

A fundamental aspect of science is prediction. The ability to predict the precise time and location of the swath of totality for a solar eclipse — many years in advance — based on our understanding of celestial physics is just one example of a success story for science. Another, from the AMS community of scientists, is our increasing ability to forecast the weather, and especially highly impactful severe weather, days in advance. This capability is a combination of increased understanding of the physical processes that influence weather; increased observational capabilities that provide the present state of the atmosphere, oceans, land surfaces, etc.; and increased computational power to take advantage of that physical understanding and observational data.

It is inconceivable that a human disaster like the Galveston hurricane of 1900 would occur today thanks to the observational and predictive power of the weather enterprise. Having predictive capabilities has been critical in reducing the loss of life and property, as well as reducing economic disruption from severe weather events.

As a reflection of the distribution of weather, climate is influenced by the same physical processes and our increasing understanding of those processes provides an increasing capability to project future changes in climate. While the characteristics of weather that matter to us most have inherent limits of predictability on the order of weeks, our understanding of the climate system shows us that projections of climate change over many years are possible. As noted in the AMS Statement on Climate Change:

“Climate projections for decades into the future are made using complex numerical models of the climate system that account for changes in the flow of energy into and out of the Earth system on time scales much longer than the predictability limit (of about two weeks) for individual weather systems. The difference between weather and climate is critically important in considering predictability. Climate is potentially predictable for much longer time scales than weather for several reasons.

“One reason is that climate can be meaningfully characterized by seasonal-to-decadal averages and other statistical measures, and the averaged weather is more predictable than individual weather events. A helpful analogy in this regard is that population averages of human mortality are predictable while life spans of individuals are not. A second reason is that climate involves physical systems and processes with long time scales, including the oceans and snow and ice, while weather largely involves atmospheric phenomena (e.g., thunderstorms, intense snow storms) with short time scales. A third reason is that climate can be affected by slowly changing factors such as human-induced changes in the chemical composition of the atmosphere, which alter the natural greenhouse effect.”

Climate models simulate the important aspects of climate and climate change based on fundamental physical laws of motion, thermodynamics, and radiative transfer. These models report on how climate would change in response to several specific “scenarios” for future greenhouse gas emission possibilities.

Future climate change projections have uncertainties that occur for several reasons — because of differences among models, because long-term predictions of natural variations (e.g., volcanic eruptions and El Niño events) are not possible, and because it is not known exactly how greenhouse gas emissions will evolve in future decades. Future emissions will depend on global social and economic development, and on the extent and impact of activities designed to reduce greenhouse gas and black carbon emissions.

While the uncertainties inherent in climate projections mean the climate will never be as predictable as a solar eclipse, the basis of those projections on known physical processes allows the scientific process to be applied rigorously, which leads to increasing confidence in the envelope of possible future climate scenarios those projections provide.

The AMS community recognizes the critical importance of developing climate change policy based on the best possible information. We stand ready to assist you and the House Science Committee to ensure that the best available scientific knowledge and understanding on climate and climate change are used in policy issues facing the nation.

———————- End Letter. ———————-

A comment about the Director’s logic

The core of it presents something resembling a syllogism.

Astronomers can accurately predict solar eclipses far in advance.

Meteorologists can accurately predict weather days in advance.

“{P}rojections of climate change over many years are possible.”

“{T}he basis of those projections on known physical processes allows the scientific process to be applied rigorously”.

“{W}hich leads to increasing confidence in the envelope of possible future climate scenarios those projections provide.”

But Dr. Seitter draws no conclusion for Chairman Smith from this chain of statements. Does this “increasing confidence” mean low but getting better — or high confidence, providing a sufficient basis for making vital public policy? They have different implications for Congress when making policy.

A climate scientist responds to the Director

Professor Roger Pielke Sr. (bio below) sent the House committee a response to Dr. Seitter’s letter, looking at key excerpts.

(1) “Hypotheses have been developed and tested through scientific experiments.”

This is incorrect. They are not doing “experiments” but are performing model-model comparisons (e.g. with and without added CO2) which is a fundamentally flawed approach as the a priori assumption is made that the natural runs are skillful. They have not, however, shown that skill. When hindcast multi-decadal model predictions are made (in which when the models are not constrained by real world observations) they do poorly as documented in numerous studies in the literature). See the ones listed in my powerpoint: “A New Paradigm for Assessing the Role of Humanity in the Climate System and in Climate Change” (2017).

(2) “Critically, independent scientists are rewarded for uncovering flaws or shortcomings in the work of their colleagues, so the scientific process is inherently self-correcting over time.”

Hardly, as exemplified by how Michael Mann behaved at the Hearing. If scientists object to the framing that Seitter presents in the letter, they are vilified or ignored. They are subsequently excluded from committees, etc that develop AMS statements and other assessments. Judy Curry and John Christy have clearly articulated this groupthink.

(3) “We can now say with very high levels of confidence, based on literally thousands of independent research efforts and multiple independent lines of evidence, that most of the warming our planet has experienced over the past 50 years is due to human activity. Indeed, to suggest that humans are not responsible for most of the warming we have experienced over the past 50 years indicates a disregard for the scientific process and the vast amount of testable evidence that has been amassed on this subject.”

This conclusion is based on the flawed assumption that the models without including added CO2 (and aerosols) can accurately predict the natural climate system. They cannot. Thus the claim of attribution is not scientifically rigorous.

(4) “Another, from the AMS community of scientists, is our increasing ability to forecast the weather, and especially highly impactful severe weather, days in advance.”

I agree, major advancements have been made. But they do not translate over into longer range forecasts, even seasonal as exemplified by the failure to predict the extreme rains in California this past winter.

(5) “As a reflection of the distribution of weather, climate is influenced by the same physical processes and our increasing understanding of those processes provides an increasing capability to project future changes in climate.”

This is wrong. Climate involves many more processes (biogeochemical, cryospheric etc) which are not important on multi-day time periods. Weather models also have initial real world observations which constrain the model predictions until that knowledge is lost as the forecast evolves. Multi-decadal climate predictions have no such constraint.

(6) He gives this excerpt from the AMS Statement text (which was made by a small subset of AMS members and not voted on by the members): “Climate is potentially predictable for much longer time scales than weather for several reasons. One reason is that climate can be meaningfully characterized by seasonal-to-decadal averages and other statistical measures, and the averaged weather is more predictable than individual weather events.”

This is also in error. The statement assumes a difference in weather and climate that does not exist. It is just the averaging time for the forecasts that matter. With weather, it is daily average temperature, for example, while for climate it could be decadal average temperature. Analyses of longer term climate data show large variations and step changes even in decadal averaged climate data.

(7) The Statement also says “A second reason is that climate involves physical systems and processes with long time scales.”

(8) “Climate models simulate the important aspects of climate and climate change based on fundamental physical laws of motion, thermodynamics, and radiative transfer.”

This is easy to show as wrong. The models have a fundamental part (e.g. pressure gradient force, advection,gravity) but clouds, precipitation, radiative flux divergence, turbulence, vegetation and so forth) are all parameterized using tuned constants and coefficients). I discuss this for one type of weather model is my book Mesoscale Meteorological Modeling (2013). The climate models are, therefore, not fundamental tools and it is erroneous to make such a claim. These models are the basis for claims on the dominance of added CO2 in changing regional and global climate.

(9) “These models report on how climate would change in response to several specific “scenarios” for future greenhouse gas emission possibilities.”

The assumption that climate models accurately predict changes in climate due to increases in just one human climate forcing is absurd. The real world climate system has more variations on multi-decadal time periods than those models produce and there are a variety of other human climate forcings that Seitter neglects. Even the AMS itself has a Statement to show this: “Inadvertent Weather Modification” (Nov 2010). I was on this Committee. But Seitter ignored it.

Thus, I urge Congressman Smith to look at Keith Seitter’s letter very critically.

Roger Pielke Sr.

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About the author

Roger Pielke Sr. is currently a Senior Research Scientist in Cooperative Institute for Research in Environmental Science. He is also an Emeritus Professor of Atmospheric Science at Colorado State University, and now serves there as a Senior Research Associate.

His list of accomplishments, honors, and publications is too long to list here. See his bio for details. See his website for commentary on climate science issues. Also see his presentations, especially these…

“In recent years the media, politicians, and activists have popularized the notion that climate change has made disasters worse. But what does the science actually say? Roger Pielke, Jr. takes a close look at the work of the Intergovernmental Panel on Climate Change, the underlying scientific research, and the data to give you the latest science on disasters and climate change. What he finds may surprise you and raise questions about the role of science in political debates.”

Interesting to read this Seiiter presentation. What I would expect from a head of the AMS, I guess. Then reading his short CV and seeing his long history of an academician and post doc background well within the confines of that institutional milleul, sure he would say what he said(whether he wrote it or not). Did they ask Pielke to come to DC from Fort Collins?
Doesn’t say but most likely not.
Spark a long awaited debate? Doubtful.

That might prove correct. But I prefer optimism. Conservatives control the Federal government and most State and local governments. Climate activists will have to change their game to get any action, debating instead of smearing their opponents.